The invention concerns an infrared (IR) spectrometer for IR spectroscopic investigation of a test sample in a first wavenumber range WB1, comprising a sample container for the test sample, wherein the sample container is transparent to IR radiation in the first wavenumber range WB1, and wherein the IR spectrometer comprises a measuring device for determining the temperature of the test sample.
Spectrometers of this type are known e.g. from devices of the MATRIX series of Bruker Optik GmbH, Ettlingen, Germany, for which heatable sample holders are available, e.g. of the type IN 601E.
Analytical information about a sample (test sample) can be obtained by means of infrared (IR) spectroscopy. The molecules in the sample absorb light energy and transform it in a characteristic fashion into oscillations of chemical bonds and rotations of individual molecular groups.
The temperature of the sample has a substantial influence on the physical and chemical behavior of the sample. The temperature not only influences the state of aggregation but also, in general, interactions within the sample (in particular, when it is a mixture of different substances). For this reason, the temperature has a significant influence on the IR spectrum of the sample. For characterization of the sample, the temperature of the sample should therefore also be detected during recording of an IR spectrum. The IR measurement preferably takes place at a predefined temperature, which is controlled during the IR measurement. A local temperature control device is typically used in the IR spectrometer for controlling the temperature of the sample.
In the simplest case, the temperature of a sample is detected by inserting a temperature sensor into the sample (e.g. immersing a thermometer into the sample fluid). This permits relatively exact measurement of the temperature. However, it may happen that the sample is thereby slightly soiled or that an undesired interaction between the temperature sensor and the sample takes place. In general, an additional cleaning step for the temperature sensor is necessary, which reduces the sample throughput.
It is also possible to position the temperature sensor not directly in the sample but in the direct vicinity of the sample, e.g. in a positioning or holding device for a sample container which contains the sample. In order to be able to gain reliable information about the temperature of the sample, the thermodynamic properties of the measuring system (sample, sample container, holding device and, if required, temperature control device) must be exactly known and, if required, controlled. Reliable temperature measurement is only possible in a state of equilibrium. It is, however, not easy to determine when the state of equilibrium has been reached. Moreover, thermal convection can easily cause systematic measuring errors.
The company leaflet “Katalog 2005—Metallblock-Thermostate and Evaporatoren” (Catalogue 2005—metal block thermostats and evaporators) of the company VLM GmbH, Leopoldshöhe-Greste, Germany, in particular page 4, discloses e.g. to arrange a sample that is contained in a sample container (e.g. a test tube) in a heating block and to measure and control the temperature of the heating block by means of a resistance thermometer of the type Pt-100. An external thermometer may additionally be used, which directly measures the temperature in the sample container. This temperature is displayed with the supplement “ST” (sample temperature).
Non-contact measurement of temperatures by means of IR radiation is also known in the art. DE 44 12 887 A1 describes measurement of the temperature of a sample in a container using IR radiation, wherein the container is made from a material that is permeable to IR radiation of a certain spectral range. The IR radiation that was emitted by the sample and has penetrated the container is guided to an IR detector by means of an optical fiber. The container is exposed to a microwave field for heating the sample.
This method is disadvantageous in that the sample must be arranged in a container that is permeable to the IR radiation of the temperature measurement, which limits the choice of materials. The IR radiation of the sample and of the container and possibly of further device components is moreover superimposed beyond the container, which aggravates evaluation of the measurement for determining the temperature. When the sample in the container is exposed to further IR radiation to perform an IR spectroscopic measurement, the determination of the temperature is further aggravated.
It is the underlying object of the present invention to provide simple and reliable measurement of the temperature of a sample in an IR spectrometer.